Native American cultures in the area included the Interior Salish, Wenatchi, Okanagan. The first white settlers began to arrive in the mid-to-late-19th century, primarily with the goal of raising livestock. One government official described the area in 1879 as, "…a desolation where even the most hopeful can find nothing in its future prospects to cheer."[4]

When railroads arrived they also brought new settlers, and the economy began a shift from ranching to dryland farming. This transition required the people to have ready access to water, and irrigation became a necessity. The first large-scale irrigation attempts began in 1898, but it would be years before real success.

The Washington State Legislature officially created Grant County February 24, 1909, and named after President Ulysses S. Grant. The county seat was located in Ephrata. The population in the county at the time was only about 8700 people.

The Columbia Basin Reclamation Project, which began as a group of businessmen from Ephrata began looking for ways to make the area more viable. One idea was to dam the Columbia River at Grand Coulee. Although the idea of the Grand Coulee Dam would not be approved until 1933 and still not implemented until 1939, the project would fundamentally change the region forever.[5][6][7]

There were 25,204 households of which 39.90% had children under the age of 18 living with them, 59.30% were married couples living together, 9.80% had a female householder with no husband present, and 25.90% were non-families. 21.20% of all households were made up of individuals and 8.90% had someone living alone who was 65 years of age or older. The average household size was 2.92 and the average family size was 3.38.

32.00% of the population were under the age of 18, 9.80% from 18 to 24, 27.00% from 25 to 44, 19.70% from 45 to 64, and 11.50% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 104.50 males. For every 100 females age 18 and over, there were 103.40 males.

The median household income $35,276, and the median family income was $38,938. Males had a median income of $32,414 versus $24,310 for females. The per capita income for the county was $15,037. About 13.10% of families and 17.40% of the population were below the poverty line, including 22.30% of those under age 18 and 9.40% of those age 65 or over.

^Symons, Lieut. Thomas W. Report of an Examination of the Upper Columbia River and the Territory in Its Vicinity in September and October, 1881, to Determine Its Navigability, and Adaptability to Steamboat Transportation: Made by Direction of the Commanding General of the Department of the Columbia. p. 121.